The discharges of populations of nerve cells tend to exhibit a degree of synchrony by virtue of their shared synaptic inputs from individual afferents. If the discharge in different afferent axons themselves show correlations the situation will be aggravated. Synchrony in the mammalian motor system leads to undesirable levels of tremor and thus it is important that we understand the potential sources of synchrony and any mechanisms that act to curb it. This program will specifically examine the problem of synchrony in the spinal cord and peripheral muscle spindle loop in the cat. A pilot study has shown that there is a tendency for gamma motoneurones themselves to exhibit synchronized discharges. The degree of correlation between gamma motoneurones of synergists, antagonists and muscles of differing function will be explored with the aim of obtaining a better understanding of the synaptic organization controlling their discharge and to assess any role that synchrony may have. Factors which tend to synchronize muscle spindle primary endings, such as a shared gamma efferent supply, synchronous firing of gamma efferents and the peripheral blood pressure pulse will be examined. The ability of the gamma efferent system to modulate or suppress synchrony between muscle spindles will be assessed. Conventional electrophysiological recording of nervous activity in decerebrated, spinal and anesthetized cats will be employed. Time series analysis of the recorded neuronal discharges will be accomplished using a micro computer. The results of the study will relate both to normal and pathological states of motor performance. In particular the mechanisms ensuring continous smooth movements will be better understood. The long term objective will be to apply this knowledge to disorders of the nervous system which are characterized by tremor or chorea.